Download The Excretory System

The Excretory System
Wastes
Metabolic wastes from cell
metabolism include:
– Salts
– Carbon dioxide
– Urea-toxic compound produced when
amino acids are used for energy
Excretion of wastes
Skin – excretes water, salts, and a small
amount of urea in sweat
Lungs – excrete carbon dioxide (produced
when sugars are broken down for ATP)
Liver – picks up amino acids in blood to
make useful compounds producing urea in
the process
Kidneys – remove urea from blood for
excretion from the body
Kidneys
Maintain homeostasis by
– Removing wastes (urea) from the blood
– Maintaining blood pH
– Regulating water content of blood
– Regulating blood volume
Kidneys &
Urinary
Tract
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Kidneys
Located on either side of the spinal
column near the lower back
The ureter (tube) carries urine from the
kidneys to the urinary bladder (which
stores the urine until it leaves the body)
Waste-laden blood enters the kidneys
through the renal artery
Kidneys filter out urea, excess water, and
other wastes which pass through the
ureter
Clean blood leaves the kidneys through
the renal vein and returns to circulation
Kidney structure
Renal medulla-inner part
Renal cortex-outer part
Nephrons-functional units of the kidney located in
the cortex
Loops of Henle-extend from cortex into renal
medulla (are extensions of nephrons)
Blood supply-arteriole, venule, capillaries
Blood enters the nephron through the arteriole,
impurities are filtered out and emptied into the
collecting duct; purified blood leaves the nephron
through the venule
Kidneys
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Nephron
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Filtration
Filtering blood takes place in the
glomerulus (a small network of capillaries
encased at the upper end of the nephron
in a Bowman’s capsule)
Fluid from blood flows into Bowman’s
capsule so the filtrate can be removed
Filtrate includes water, urea, glucose,
salts, amino acids, some vitamins
All blood is filtered every 45 minutes
Reabsorption
Some materials removed in Bowman’s
capsule will be reabsorbed including amino
acids, fats, glucose, and 99% of the water
Remaining material (urine) is drained into
a collecting duct and runs into the Loop of
Henle where urine volume is minimized
(by more reabsorption of water)
Purified blood returns to circulation
Urine is transferred to the urinary bladder
and excreted through the urethra
Control of kidney function
Controlled mainly by composition of
blood and regulatory hormones
released due to the composition of
blood